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Temperature is Average Thermal Energy

by Ron Kurtus (revised 1 April 2007)

The thermal energy of an object consists of the total kinetic energy of all its atoms and molecules. The temperature of the object is a measurement average intensity of its thermal energy. The lower limit of temperature is when the kinetic energy of the particles approaches zero. This temperature is called absolute zero. The upper temperature limit is determined by the maximum possible velocity of it particles. Temperature is measured with a device called a thermometer that gives relative readings of how hot or cold an object is.

Questions you may have include:

• What is the intensity of thermal energy?
• What are the temperature limits?
• How is temperature measured?

This lesson will answer those questions. There is a mini-quiz near the end of the lesson.

Useful tools: Metric-English Conversion | Scientific Calculator.

Temperature is intensity of thermal energy

The temperature of an object is the average intensity of its thermal energy.

The thermal energy of an object is the total kinetic or moving energy of all its particles, plus their potential energy. This is different than heat, which is the flow of thermal energy from one object to another.

The intensity of thermal energy is the average kinetic energy of the object. That average is the energy of a typical particle in the object. Its equation is:

KE_a = ½ mv²

where:

• KE_a is the average kinetic energy of all the particles
• m is the mass of a single particle or molecule
• v is the average velocity of all the particles
• v² is the velocity squared or velocity times itself
• ½ mv² is ½ times m times v²

(See Thermal Energy for more information on this subject.)

The kinetic energy is measured in joules. Since it is difficult to determine the average kinetic energy of a measure the intensity of thermal energy, temperature is used as a relative measurement of that intensity.

Temperature limits

There are upper and lower limits to temperature.

Upper limit

The highest possible temperature is limited by the greatest speed possible for a particle of matter, which is the speed of light. According to the Theory of Relativity, matter can approach that speed but never reach it.

The thermal energy is determined by Einstein's famous E = mc² equation.

Lower limit

The lowest or coldest temperature possible is called Absolute Zero. This absolute zero limit is the temperature of an object when all of its matter has zero energy.

Quantum Mechanics laws state that Absolute Zero can be approached but never reached, because matter cannot have zero energy.

(See Temperature Limits for more information on this subject.)

Measurement of temperature

Temperature is measured with a thermometer. This is a device that records changes when subjected to varying temperatures. The most common thermometer measures the expansion of a liquid with the change in temperature.

Heat is transferred from an object to the thermometer until they are both at the same temperature.

Temperature scales

A scale is added to the thermometer, in order to give readings of the relative temperature. In the Celsius scale, the freezing point of water is set at 0° C (zero degrees Celsius) and the boiling point of water is set at 100° C. The scale is divided into 100 units of temperature, called degrees.

Other temperature scales are the Fahrenheit, Kelvin and Rankine scales.

(See Temperature Measurement: Thermometers for more information on this subject.)

Summary

Temperature is the average intensity of the thermal energy of an object. The lower limit of temperature is called absolute zero. The upper temperature limit is determined by the speed of light. Temperature is measured with a device called a thermometer that gives relative readings.

Answers to Readers' Questions

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Resources

The following resources provide information on this subject:

Websites

Physical Science Resources

Books

Top-rated books on Thermal Energy

Top-rated books on Temperature

Miscellaneous

Mini-quiz to check your understanding

1. What is the difference between temperature and thermal energy?

2. What limits the greatest possible temperature?

3. Why is a scale added to a thermometer?

If you got all three correct, you are on your way to becoming a Champion in Physical Science. If you had problems, you had better look over the material again.

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Temperature is Average Thermal Energy